In producing farming plants having novel characteristics, which can develop an agricultural field, expression of a foreign gene (i.e., transgene) to be introduced into a plant body is greatly influenced by transcriptional, post-transcriptional, translational and post-translational elements. Among said elements, particularly, a promoter belonging to the transcriptional elements is the most important element, which not only can directly influence a transcription of a transgene to ultimately change the expression level, but also can change the steps of expressing a transgene, or the tissue- or cell-specificities. To date, although numerous promoters have been isolated from various plants for expression of a trangene, only a few promoters among them are currently practically used for transformation of a plant body. CaMV (cauliflower mosaic virus) 35S promoter and its derivatives, which have been most widely used in this field at present, induce an extensive expression of genes in the whole tissues of a plant body and, exhibit a high activity especially in vascular tissues and most cells of roots and leaves. However, the CaMV 35S promoter exhibits lower activity in monocot plants such as rice plant, etc., than in dicot plants, and even does not exhibit any activity in certain cells such as pollen, etc. Numerous promoters other than CaMV 35S promoter, which have originated from dicot plants, have also been used for transformation of monocot plants, but exhibit lower activity than do promoters originating from monocot plants. Further, rbcS (ribulose bisphosphate carboxylase /oxygenase small subunit) promoter of rice plant, Act1 (actin1) promoter of rice plant, and Ubi1 promoter of maize plant have been investigated as a promoter useful for transformation of monocot plants. Among them, Act1 and Ubi1 promoters exhibit relatively a high activity in monocot plants as compared to CaMV 35S promoter, and therefore, have been generally used for transformation of monocot plants. However, Ubi1 promoter exhibits activity in numerous types of cells but does not cover the whole tissues of a plant body. Moreover, although Ubi1 promoter exhibits a strong activity especially in young roots, its activity is greatly reduced as the roots grow. In addition, Act1 promoter exhibits activity mainly in the elongating tissues and reproductive tissues. Thus, said promoters are not effective for expression of a ubiquitous gene in monocot plants.
Therefore, there exists a continuous necessity for developing a promoter showing a strong, stable and ubiquitous activity in transforming monocot plants.